Crosslinkable rigid-rod benzobisazole copolymer

ABSTRACT

There are provided para-ordered aromatic heterocyclic copolymers having repeating groups of the following formulas: ##STR1## wherein a, b, c, d, and e are positive integers, each representing an average number of the respective different recurring units present in the repeating group, m and n are 1 or 2, R and R&#39; are alkyl groups having 1 to 4 carbon atoms, and Q is a benzobisazole group of the formula: ##STR2## wherein Y is --O--, --S--, or --NH--. In the copolymers wherein m or n is 2, the R or R&#39; groups can be the same or different. In copolymer I, the ratio a:b can be about 1:1 to 99:1. In copolymer II, the ratio c:(d+e) can be about 1:1 to 99:1, and the ratio d:e can be about 1:99 to 99:1.

RIGHTS OF THE GOVERNMENT

The invention described herein may be manufactured and used by or forthe Government of the United States for all governmental purposeswithout the payment of any royalty.

This is a division of application Ser. No. 379,038, filed July 13, 1989,now U.S. Pat. No. 5,003,035.

BACKGROUND OF THE INVENTION

This invention relates to crosslinkable, para-ordered aromaticheterocyclic copolymers.

In general, the class of aromatic heterocyclic extended chain copolymersare well known for their outstanding thermal, physical and chemicalproperties. These copolymers generally exhibit excellent modulus andtenacity properties, but lack good properties when in compression, whichlimits their use as reinforcing structurall fibers.

In Tsai et al, U.S. Pat. No. 4,835,246, dated May 30, 1989, we disclosepara-ordered aromatic heterocyclic polymers having pendant benzazolegroups. These polymers exhibit improved compressive properties. Furtherresearch into para-ordered aromatic heterocyclic polymers has providedcopolymers which are crosslinkable without degradation of the maincopolymer backbone.

It is an object of the present invention to provide novel crosslinkablerigid-rod aromatic heterocyclic copolymers.

Other objects, aspects and advantages of the present invention will beapparent to those skilled in the art from a reading of the followingdetailed disclosure of the invention.

SUMMARY OF THE INVENTION

In accordance with the present invention, there are providedpara-ordered aromatic heterocyclic copolymers having repeating groups ofthe following formulas: ##STR3## wherein a, b, c, d, and e are positiveintegers, each representing an average number of the respectivedifferent recurring units present in the repeating group, m and n are 1or 2, R and R' are alkyl groups having 1 to 4 carbon atoms, and Q is abenzobisazole group of the formula: ##STR4## wherein Y is --O--, --S--,or --NH--. In the copolymers wherein m or n is 2, the R or R' groups canbe the same or different. In copolymer I, the ratio a:b can be about 1:1to 99:1. In copolymer II, the ratio c:(d+e) can be about 1:1 to 99:1,and the ratio d:e can be about 1:99 to 99:1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The copolymers of the present invention are prepared by reacting anamine monomer having the structure ##STR5## with terephthalic acid andone or more mono- or di-alkyl-substituted terephthalic acid(s). Aterephthalyl halide or terephthalonitrile may be employed in place ofthe terephthalic acid or the mono- or di-alkyl-substituted terephthalicacid.

The pendant alkyl terephthalic acid monomers may be prepared as follows:##STR6##

In the reactions given above, R and n are as previously defined.

Conversion of the mono- or di-alkyl-p-dihalo benzene to thecorresponding pendant alkyl p-dinitrile, with subsequent conversion tothe carboxylic acid or acid halide is known in the art.

The copolymers may be prepared by:

a. mixing an amino monomer, as described above, with or withoutoxidation protecting atoms or groups, e.g., HCl groups, with apreliminary solvent of phosphoric acid having a relatively lowphosphorous pentoxide content, about 63 to 83%, preferably below about80%.

b. heating and optionally placing the resulting mixture under reducedpressure to remove any volatile protecting atoms or groups present andprovide a mixture of the amino monomer in the preliminary solvent. Thisstep, as well as subsequent steps, is preferably carried out under aninert gas atmosphere. Suitable inert gases include helium, nitrogen, andargon. Heating the mixture to about 60°-80° C. for about 6 to 24 hoursis generally sufficient to remove any volatile products.

c. adding a mixture of the terephthalic acid and alkyl-substitutedterephthalic acid or acid salt monomers to the mixture resulting fromstep b to provide a mixture of amino monomer and acid monomers in thepreliminary solvent.

d. increasing the phosphorous pentoxide content of the mixture resultingfrom step c to provide a reaction medium in which the percentage ofphosphorous pentoxide should be about 82 to 86% P₂ O₅, preferably about82 to 84% at the end of the copolymerization.

e. causing copolymerization of the monomers at a temperature of about100° to 200° C. for about 18 to 36 hours. In a presently preferredembodiment, the reaction temperature is increased gradually during thereaction period, e.g., 170° C. for 20 hours, then 190° C for 4 hours.

The dinitrile and diacid halide monomers tend to sublimate at elevatedtemperatures; accordingly, it is desireable to maintain the mixtureresulting from step d at a relatively lower temperature, e.g., about 90°C. for about 4 to 16 hours to generate oligomers prior to heating themixture to the higher copolymerization temperatures.

Optionally, steps a, b and c may be combined by adding the amino andterephthalic acid and/or acid salt monomers to the preliminaryphosphoric acid solvent, then removing any volatiles, after which the P₂O₅ content is raised and the copolymerization is carried out.

At the end of the reaction period, the copolymer may be precipitatedfrom solution by pouring the reaction mixture into water. The copolymeris treated with a weak base, such as ammonium hydroxide, then purifiedby washing with water and methanol until all phosphoric acid is removed.The copolymer is then dried under reduced pressure.

The copolymer may be further purified by dissolving it inmethanesulfonic acid, filtering, inversely precipitating with methanol,stirring with concentrated ammonium hydroxide, and washing with water.The ammonia-free water solution is then filtered and the copolymerwashed with methanol and methanol-benzene mixtures, gradually changingto 100 percent benzene. The swollen copolymer is frozen and finallydried under reduced pressure to give a purified copolymer having a highmolecular weight.

The copolymer compositions of this invention are optically anisotropic,i.e., microscopic regions of a given extended chain composition arebirefringent; a bulk extended chain composition sample depolarizesplane-polarized light because the light transmission properties of themicroscopic areas of the extended chain composition vary with direction.This characteristic is associated with the existence of at least part ofthe extended chain copolymer compositions in the liquid crystalline ormesomorphic state.

The extended chain copolymer compositions of this invention that exhibitoptical anisotropy do so while the extended chain copolymer compositionsare in the relaxed state. This in in contrast to conventional copolymersolutions which may be caused to depolarize plane-polarized light whensubjected to appreciable shear.

The copolymers of this invention can be crosslinked by exposure to anelevated temperature or by exposure to suitable radiation. Crosslinkingby exposure to heat may be accomplished by exposing the material to atemperature of about 300°-550° C. for about 10 to 60 sec. At the highertemperatures, an inert atmosphere of nitrogen, helium or the like,surrounding the material is advised. Radiation crosslinking may beaccomplished by exposure of the material to a suitable radiation source,such as gamma radiation, at a radiation level for a time sufficient toprovide an irradiation dosage of about 0.1 to 2 GRad.

The copolymers of this invention are soluble in strong acids. such assulfuric acid and methanesulfonic acid. After crosslinking, they arecompletely insoluble in all acid solvents.

The liquid crystalline extended chain copolymer compositions areextremely suitable for spinning into highly ordered and high strengthfibers by spinning them into suitable baths such as by wet and "air gaP"spinning techniques, using spinnerets and other apparatus constructed ofmaterials resistant to the strong acids used. In "air gap" spinning, thespinneret is usually located in air or in an inert gaseous medium ashort distance. e.g., 1 to 24 cm, above the surface of a coagulatingbath. Techniques for fiber spinning are well known in the art. Suchfibers are useful as reinforcement substitutes for other inorganic ororganic products.

The copolymers of this invention may also be employed in any usetypically performed by engineering thermoplastic materials, such a metalreplacements and those areas where high performance is necessary.

Intrinsic viscosity is determined by extrapolation of η(rel) -1/c and 1n η(rel)/c to zero concentration in methanesulfonicacid at 30° C.

The following examples illustrate the invention:

EXAMPLE ICopoly((benzo(1,2-d:4,5-d')bisthiazole-2,6-diyl))-(p-phenylene)50%/(2-methyl-p-phenylene)50%)

Into the bottom of a resin flask equipped with a high torque mechanicalstirrer, nitrogen inlet/outlet, pressure regulator and a side openingfor additions, was placed 3.3823 g (14 mmol) of2,5-diamino-1,4-benzenedithiol dihydrochloride, 1.1460 g (7 mmol) ofterephthalic acid, 0.9806 g (7 mmol) of 2,5-biscyanotoluene and 19.5 gof polyphosphoric acid (PPA) (77% P₂ O₅). The monomers were incorporatedinto the PPA by stirring, and the resulting mixture was thendehydrochlorinated under reduced pressure (176 mm) by heating asfollows: 45° C./18h; 78° C./8h; 80° C./16h; and 90° C./4h. The reactionmixture was cooled to 50° C. and 8.10 g of P₂ O₅ was added, therebyraising the final copolymer concentration to 12%. Under a positivenitrogen flow, the mixture was heated at 170° C. for 20h then at 190° C.for 4h. As the temperature was increased, opalescence began to appear atabout 160° C. The copolymer was precipitated into water, collected bysuction filtration, washed with ammonium hydroxide, water, and methanoland then dried under reduced pressure (0.02 mm) at 110° C. An intrinsicviscosity of 31 dl/g was obtained in methanesulfonic acid.

Calcd for C₂₉ H₁₄ S₄ N₄ : C, 63.69: H, 2.57; N, 10.02; S, 23.44.

Found: C, 61.35: H 2.54: N, 10.31, S, 22.17.

EXAMPLE IICopoly((benzo(1,2-d:4,5-d')bisthiazole-2,6-diyl))-(P-phenylene)90%/(2-methyl-P-phenylene)10%)

Into the bottom of a resin flask equipped with a high torque mechanicalstirrer, nitrogen inlet/outlet, pressure regulator and a side openingfor additions, was placed 5.0394 g (21 mmol) of2,5-diamino-1,4-benzenedithiol dihydrochloride, 3.0729 g (18 mmol) ofterephthalic acid, 0.2922 g (2 mmol) of 2,5-biscyanotoluene and 18.3 gof PPA (77% P₂ O₅). The monomers were incorporated into the PPA bystirring, and the resulting mixture was then dehydrochlorinated underreduced pressure (176 mm) by heating as follows: 45° C./18h; 78° C./8h;80° C./16h; and 90° C./ 4h. The reaction mixture was cooled to 50° C.and 19.4 g of P₂ O₅ was added, thereby raising the final copolymerconcentration to 12%. Under a positive nitrogen flow, the mixture washeated at 170° C. for 20h then at 190° C. for 4h. As the temperature wasincreased, opalescence began to appear at about 160° C. The copolymerwas precipitated into water, collected by suction filtration, washedwith ammonium hydroxide, water, and methanol and then dried underreduced pressure (0.02 mm) at 110° C. An intrinsic viscosity of 32 dl/gwas obtained in methanesulfonic acid. Calcd for C₁₄.1 H₆.2 S₂ N₂ : C,63.25: H, 2.33; N, 9.15; S, 23.94.

Found: C, 61.75: H, 2.51; N, 10.6; S, 22.79.

EXAMPLE III

Copoly((benzo(1,2-d:4,5-d')bisthiazole-2,6-diyl))-(p-phenylene)98%(2-methyl-P-phenylene)2%)

Into the bottom of a resin flask equipped with a high torque mechanicalstirrer, nitrogen inlet/outlet, pressure regulator and a side openingfor additions, was placed 10.4616 g (43 mmol) of2,5-diamino-1,4-benzenedithiol dihydrochloride, 6.9464 g (42 mmol) ofterephthalic acid, 0.1213 g (1 mmol) of 2.5-biscyanotoluene and 48.5 gof PPA (77% P₂ O₅). The monomers were incorporated into the PPA bystirring, and the resulting mixture was then dehydrochlorinated underreduced pressure (176 mm) by heating as follows: 45° C./18h; 78° C./8h;and 90° C./4h. The reaction mixture was cooled to 50° C. and 32.0 g ofP₂ O₅, was added, thereby raising the final copolymer concentration to12%. Under a positive nitrogen flow, the mixture was heated at 170° C.for 20h then at 190° C. for 4h. As the temperature was increased,opalescence began to appear at about 160° C. The copolymer wasprecipitated into water, collected by suction filtration, washed withammonium hydroxide, water, and methanol and then dried under reducedpressure (0.02 mm) at 140° C. for 24 h. An intrinsic viscosity of 29.5dl/g was obtained in methanesulfonic acid.

Calcd for C₁₄.02 H₆.04 S₂ N₂ : C, 63.15: H, 2.28; N, 10.05; S, 24.06.

Found: C, 61.52: H; 2.49; N, 11.10; S, 23.00.

EXAMPLE IVPoly(benzo(1,2-d:4.5-d')bisthiazole-2,6-diyl(2-methyl-p-phenylene))

This Polymer does not form a part of the present invention. It isincluded here for comparison.

Into the bottom of a resin flask equipped with a high torque mechanicalstirrer, nitrogen inlet/outlet, pressure regulator and a side openingfor additions, was placed 2.6793 g (11 mmol) of2,5-diamino-1,4-benzenedithiol dihydrochloride, 1,5533 g (11 mmol) of2,5-biscyanotoluene and 20.40 g of PPA (77% P₂ O₅). The monomers wereincorporated into the PPA by stirring, and the resulting mixture wasthen dehydrochlorinated under reduced pressure (176 mm) by heating asfollows: 45° C./18h; 78° C./8h; 80° C./16h. The reaction mixture wascooled to 50° C. and 5.34 g of P₂ O₅ was added, thereby raising thefinal polymer concentration to 13%. Under a positive nitrogen flow, themixture was heated at 90° C. for 16h, at 170° C. for 24h and at 190° C.for 6h. As the temperature was increased, opalescence began to appear atabout 160° C. The polymer was precipitated into water, collected bysuction filtration, washed with ammonium hydroxide, water, and methanoland then dried under reduced pressure (0.02 mm) at 110° C. An intrinsicviscosity of 23.0 dl/g was obtained in methanesulfonic acid.

Calcd for C₁₅ H₈ S₂ N₂ :C, 64.26: H, 2.87; N, 9.99; S, 22.80. Found: C,64.61: H, 3.06; N, 9.96; S, 22.08.

EXAMPLE V

Poly(benzo(1,2-d:4,5-d')bisthiazole-2,6-diyl (2,5-dimethyl-p-phenylene))

This polymer does not form a part of the present invention. It isincluded here for comparison.

Into the bottom of a resin flask equipped with a high torque mechanicalstirrer, nitrogen inlet/outlet, pressure regulator and a side openingfor additions, was placed 4.835 g (20 mmol) of2.5-diamino-1,4-benzenedithiol dihydrochloride and 35.50 g of PPA (77%P₂ O₅). The monomer was incorporated into the PPA by stirring, and theresulting mixture was then dehydrochlorinated under reduced pressure(176 mm) by heating as follows: 45° C./18h; 78° C./8h; 80° C./16h; and90° C./4h. At the end of this heating, a clear solution was obtainedindicating the completion of dehydrochlorination. The reaction mixturewas cooled to 50° C. and 4.5604 g (20 mmol) of 2.5-dimethyl terephthalylchloride and 16.0 g of P₂ O₅ were added, with continuous stirring,thereby raising the final copolymer concentration to 10%. Under apositive nitrogen flow, the mixture was heated at 80° C. for 16h. at150° C. for 20 h and at 190° C. for 4h. The copolymer was precipitatedinto water, collected by suction filtration washed with ammoniumhydroxide, water, and methanol and then dried under reduced pressure(0.02 mm) at 110° C. An intrinsic viscosity of 30.8 dl/g was obtained inmethanesulfonic acid.

Calcd for C₁₆ H₁₀ S₂ N₂ : C, 65.28: H, 3.42; N, 9.51; S, 21.78.

Found: C, 64.77: H, 3.41; N, 9.38; S, 20.37.

EXAMPLE VI Mechanical Properties, Solubility and Crosslinking

For comparison, the intrinsic viscosities of the polymers and copolymersprepared in Examples I-V are shown in Table I, below. For convenience,the structure of copolymer I is shown:

                  TABLE I                                                         ______________________________________                                         ##STR7##                                                                     Polymer Mole %                                                                Ex.   a       b          R     R'    Conc. η                              ______________________________________                                        I     50      50         CH.sub.3                                                                            H     12    31                                 II    90      10         CH.sub.3                                                                            H     12    32                                 III   98       2         CH.sub.3                                                                            H     12    29                                 IV     0      100        CH.sub.3                                                                            H     13    23                                 V      0      100        CH.sub.3                                                                            CH.sub.3                                                                            10    31                                 ______________________________________                                    

In the table above, the term Conc. means the weight Percentconcentration of polymer in the polymerization media (PPA). Theintrinsic viscosities (η) were measured in methanesulfonic acid MSA) at30° C.

The copolymers prepared according to examples I-V were spun from the PPAdope into monofilament fibers using a dry-jet wet spinning method with a10 mil., diameter spinnerette and coagulated in distilled water. Thebulk viscosity and processing conditions for each dope are shown inTable II, below. The air gap where the fiber was stretched wasmaintained at 8 in. After neutralization with 3% NH₄ OH solution andwashing with water, the fibers were tension dried at 150° C. and heattreated in a tube oven with 30 sec. residence time under nitrogen,except as noted.

Tensile properties were measured using an Instron tensile tester with 1,3 and 5 ft. gauge length for the correction of machine compliance.Compressive strength was measured on single-filament fiber at 1 ft.gauge length using the recoil method.

                  TABLE II                                                        ______________________________________                                        Processing Conditions, Mechanical Properties and Solubility                             Physical Properties                                                             HT      Mod   TS    E.sub.b                                                                             CS    Solubility                        Ex.  SDR    °C.                                                                            (msi) (ksi) (%)   (ksi) in MSA                            ______________________________________                                        I     8     500     33    290 ±                                                                            1.0 ±                                                                            25-46 Swelled                                                     12    0.1                                                 8      500*   38    341 ±                                                                            1.0 ±                                                                            12-25 Swelled                                                     33    0.1                                                30     500     41    465 ±                                                                            1.3 ±                                                                            19-30 Swelled                                                     24    0.1                                                30      500*   43    404 ±                                                                            1.2 ±                                                                            12-30 Swelled                                                     30    0.1                                           II   18     500     28    240 ±                                                                            1.8 ±                                                                            66-75 Swelled                                                     32    0.6                                           III  20     500     31 ± 4                                                                           350 ±                                                                            1.5 ±                                                                            37-43 Swelled                                                     43    0.3                                           IV    8     500     32 ± 2                                                                           270 ±                                                                            1.7 ±                                                                            47-53 Swelled                                                     26    0.2                                                51     500     31 ± 2                                                                           344 ±                                                                            1.7 ±                                                                            20-30 Swelled                                                     30    0.2                                           V    19     350     17    306 ±                                                                            2.8 ±                                                                            --                                                                43    0.3                                                --     275     --    --    --    --    Soluble                           ______________________________________                                         *heat treated in air atmosphere                                          

Various modifications may be made to the invention as described withoutdeparting from the spirit of the invention or the scope of the appendedclaims.

We claim:
 1. A para-ordered optically anisotropic aromatic heterocycliccopolymer having repeating groups of the formula: ##STR8## wherein a andb are positive integers, each representing an average number of therespective different recurring units present in said repeating group, mis 1 or 2, R is an alkyl group having 1 to 4 carbon atoms, and Q is abenzobisazole group of the formula: ##STR9## wherein Y is --O-- or--NH--.
 2. The copolymer of claim 1 wherein the ratio of a:b is about1:1 to 99:1.
 3. The copolymer of claim 1 wherein Y is --O--.
 4. Thecopolymer of claim 3 wherein m is
 1. 5. The copolymer of claim 3 whereinm is
 2. 6. The copolymer of claim 1 wherein Y is --NH--.
 7. Thecopolymer of claim 6 wherein m is
 1. 8. The copolymer of claim 6 whereinm is
 2. 9. A para-ordered optically anisotropic aromatic heterocycliccopolymer having repeating groups of the formula: ##STR10## wherein c, dand e are positive integers, each representing an average number of therespective different recurring units present in said repeating group, mand n are 1 or 2, R and R' are alkyl groups having 1 to 4 carbon atoms,and Q is a benzobisazole group of the formula: ##STR11## wherein Y is--O-- or --NH--.
 10. The copolymer of claim 9 wherein the ratio ofc:(d+e) is about 1:1 to 99:1 and the ratio of d:e is about 1:99 to 99:1.11. The copolymer of claim 9 wherein Y is --O--.
 12. The copolymer ofclaim 11 wherein m is 1 and n is
 1. 13. The copolymer of claim 11wherein m is 1 and n is
 2. 14. The copolymer of claim 11 wherein m is 2and n is
 1. 15. The copolymer of claim 11 wherein m is 2 and n is
 2. 16.The copolymer of claim 9 wherein Y is --NH--.
 17. The copolymer of claim16 wherein m is 1 and n is
 1. 18. The copolymer of claim 16 wherein m is1 and n is
 2. 19. The copolymer of claim 16 wherein m is 2 and n is 1.20. The copolymer of claim 16 wherein m is 2 and n is 2.